Electron discharge device



Feb. 16, 1932. R. M. BURNS ELECTRON DISCHARGE DEVICE Filed July 50, 1926Cod/7);; flan /7 5e 041a Mariya/me ox/de lnvenfor: Z I EobZZ/jfiurns.

' W Af/amey Patented Feb. 16, 1932 UNITED STATES PATENT OFFICE ROBERT M.BURNS, OF BROOKLYN, NEW YORK, ASSIGNOR T BELL TELEPHONE LABORA- TORIES,INCORPORATED, 013 NEW YORK, N. Y., A CORPORATION OF N EW'YORK ELECTRONDISCHARGE DEVICE Application filed July 30, 1926. Serial No. 125,873.

An object of the invention is to improve the operating characteristicsof electron discharge devices.

When electron discharge devices having I thermionically active cathodesare operated at high temperatures, there is a tendency for particles ofthe active material with which the cathodes are coated to deposit on thecontrol electrodes or grids. Such deposit prevents the proper operationof the device, since the grid becomes a secondary emitter of electronsand causes a blocking effect on the electron stream from the cathode tothe anode.

A method for reducing this blocking or paralyzing effect by coating thegrid with nickel oxide by oxidation at a suitable temperature isdisclosed in M. J. Kelly, Patent 1,432,867, issued October 24, 1922. Asimilar result is obtained by calorizing the metal grids with aluminumand aluminum oxide, to provide a coating which combines with the activematerials emitted from the cathode to form stable compounds, and therebyprevent secondary emission from the grid. This method is disclosed inPatent No. 1,722,121, issued July 23, 1929 to J. R. Wilson. It is alsoknown that the use of a nickel-chromium alloy grid structure, asdisclosed in J. E. Harris Patent 1,601,066, issued September 28,

1926, prevents secondary emission from the grid due to the chromic oxidecombining with the basic oxides emitted by the filament to formchromites which are stable compounds.

The present inventionvrelates to a coating for electrodes which will notreadily decompose and also to a method of coating electrodes. I

As an electrode coating the invention has its specific embodiment in agrid of an electron discharge device coated with manganese oxide. 7

As a method the invention is embodied specifically, in an electrolyticdeposition process whereby a highly electro-negative metallic coating isobtained by electro-depositionfrom an aqueous salt solution. Suchcoating may then be oxidized to form a coalescent acidic oxide coating.In the application of this process, an improved electrode coating isproduced by GlBCtIO-dGPOSltlOIl.

The term electro-negative is used throughout the specification todesignate the metals above hydrogen in the electro-motiveseries ofmetals as defined on page 1565, Standard handbook of electricalengineers, 1915, which assume a negative potential in an electrolyticsolution. I

The coating or plating is produced on the electrode preferably byimmersing it in an electrolytic bath containing an electro-negativematerial in the form of a salt, such as manganese sulphate or chloride,together with a good conductingsalt, such as ammonium sulphate orchloride, and an acidifying agent, such as sulphuric acid. The anodicelement of the bath consists of an inert material which is immersed inthe bath surrounded by a cylinder of refractory material to preventexcessive oxidation of the bath, and also to form a partition for theanolyte andcatholyte. The material to be electrolyzed,-namely, theelectrode, forms the cathodic element of the bathand is immersed in thecatholyte surrounding the refractory cylinder. The bath is maintained ata low temperature and a relatively high current density to form acontinuous coalescent surface on the cathodic element. Upon removal fromthe bath the electrode readily oxidizes upon coming into contact withthe air to a degree depending on the conditions of theelectro-deposition which may be varied to obtain any desirable amount ofoxidation. The coating on the electrode is comparable with nickelplating and forms a hard, continuous and adherent surface which will notflake. Furthermore, when mounted in an electron discharge device andheated by bombardment, the oxidized surface of the elec-. trode will notdecompose nor will the surface become brittle. In fact, more of themetallic manganese is changed to. the oxide to provide a sufficientamount of manganese oxide to react with the thermionically activeparticles emitted from the cathode to form inactive compounds which arestable.

A satisfactory bath may consist of 600 grams of manganese chloride,MNCLQ. 4H' O; 10 ams ammonium chloride, NH GL; 2.5 grams of sulphuricacid; and

water for each liter of solution. This bath is preferabl contained in anon-conducting vessel suc 1 as a glass jar. An anode of inert material,such as graphite, is inserted in the bath and is surrounded by a porousnon-conducting cylinder, preferably of alundum. This cylinder preventsexcessive oxidation of the bath and forms a partition wall between theanolyte surrounding the anode and the catholyte surrounding thecylinder.

The electrode to be electrolyzed is inserted in the catholyte and formsthe cathode element of the electrolytic bath. The cathode and anode areconnected together by an external source of voltage of approximately 4volts. The bath is maintained at a low temperature of from 5 to 10degrees centigrade, and a current density of between 7 0 and 125 amperesper square decimeter. The low temperature and high current densitygoverns the electrolytic action of the bath, whereby the nature of thedeposit can be more easily controlled and the coating will be continuousand adherent on the metal electrode which is being plated.

The process of obtaining a continuous and coalescent acidic oxidecoating on the electrode is as follows: Before the electrode is insertedin the electrolyte hereinbefore menn: tioned, it is cleansed in analkali bath which Fill may consist of a solution of sodium hydroxide orother alkali salts. After this preliminary cleaning, the electrode isimmersed in a dilute nitric acid solution, consisting of one part waterand one part of nitric acid, to thoroughly clean the metallic surface ofthe electrode. The electrode is then immersed in the electrolytic bathof the electro-negative substance for a period of from 10 to 30 minutes.By this process there is formed a continuous coating of metallicmanganese on the electrode which is comparable with nickel plating. Uponremoval from the bath the electrolyzcd electrode slowly oxidizes in theair to form a superficial coating of manganese oxide which is an acidicoxide and is light gray in color. The amount of oxide coating which maybe formed on the electro-plated surface depends on the controllingfactors of W temperature and current density at which the bath ismaintained during the electrolytic process. For instance, at lowercurrent densities, other than those given above, the deposit is nearlyblack in color with a heavy coating of oxide.

The drawing illustrates one form of an electron discharge device havingan electrode or grid made in accordance with this invention, aprotective coating on the grid preventing that electrode from becoming asource of secondary electrons.

The discharge device, as illustrated, consists of an evacuated vessel 10to which the usual base portion 11 supporting the terminals 12 isattached. Within the vessel 10 is a glass stem 13 from which an arbor orpost 14 arises. This arbor 14 provides means for supporting a nickelanode 15, a nickel grid 16, and a cathode 17 coated with thermionicallyactive material preferably basic oxides of the alkaline earth group ofmetals. The anode, as shown, is in the form of'aflattened cylinder andis supported by suitable wires (not shown) extending from the arbor 14.The anode 15 surrounds the grid 16 and the cathode 171 The grid 16 issupported from the arbor 14 by wires 18 and the cathode is supported atone end, from the arbor 14, by wires 19 and at the lower end by means ofwires 20, 21 and 22. The wires and 22 also serve as leading-in wires forthe current applied to the cathode. \Vires 23 and 24 are leading-inwires connecting respectively to the plate and the grid. \Vhile themechanical arrangement of the electrodes within the illustrated tubehave been described, it is to be understood that the invention is notlimited to this particular type of tube, which is shown merely for thepurpose of illustrating one form of an electron discharge device towhich this invention is applicable.

In the manufacture and assembly of the electrodes in the evacuatedvessel, the electrodes and the vessel are subjected to an evacuationprocess to remove occluded gases and Water vapor. During this processthe elec trodes are heated to a dull redcolor to in crease theevacuation of gases. This heatingmay be utilized to further oxidize themetallic manganese plating on the grid and thereby increase the oxidecoating so that the oxide content of the grid will be substantially.greater than the metallic manganese content. After the evacuationprocess is completed the tube is sealed at the tip and the device isready for use. The coating on the grid will be found to be relativelyhard and coalescent and will not chip or flake in the operation of thedevice.

By thus coating the grid electrode in the manner above described, theparticles of thermionically active material which may be emitted fromthe cathode and deposited on the grid, will not render the gridthermionically active since the acidic oxide coating will combine withthe basic oxides of the material thrown upon the grid and thereby forminactive stable compounds, presumably manganites. Furthermore, theacidic oxide readily reacts with'the thermionic oxides so that thecompounds are formed instantaneously upon contact.

While the detailed description of the invention is directed to a methodof forming the electro-negative metal and acidic oxide on a base metalsuch as nickel, the invention is not limited to base metals, since theelectrodeposition may be produced on any metallic surface.

III)

What is claimed is: V

1. A coating for an electrode of an electron discharge device consistingof a thin layer comprising metallic manganese.

2. A coating for an electrode of an electron discharge device comprisinga surface layer of partially oxidized manganese.

3. An electrode for an electron discharge device having a coalescentcoating comprising electro-deposited metallic manganese.

l. An electrode for an electron discharge device having a coating ofelectro-deposited metallic manganese at least partially oxidized.

5. An electron discharge device comprising a thermionically activecathode, and another electrode, said other electrode having anelectro-deposited coating consisting of manganese and manganese oxidewhich combines with particles from said cathode to form stablecompounds.

6. An electron discharge device comprising a cathode having a coatingcontaining a thermionically active basic oxide, and another electrodehaving a coating of partially oxidized manganese which forms a stablethermionically inactive compound with said basic oxide.

7. An electron discharge device comprising a cathode, a grid, and ananode, said grid having an electro-deposited coating consisting ofmanganese and manganese oxide.

8. An electron discharge device comprising a cathode, a grid and ananode, said grid having a coating comprising manganese oxide.

9. An electron discharge device comprising a cathode, a grid, and ananode, said grid having a coalescent coating comprisingelectro-deposited metallic manganese.

10. An electron discharge device comprising a cathode having a coatingcontaining a thermionically active basic oxide, a grid and an anode,said grid having a coating comprising manganese oxide Which forms astable thermionicallyinactive compound with said basic oxide.

In witness whereof, I hereunto subscribe my name this 27th day of JulyA. D., 1926.

ROBERT M. BURNS.

